Start the test ride by adjusting the seat height, and during the ride try accelerating, braking, shifting, fork action. All other things being equal, trust your intuition and choose the bike you feel most comfortable on!
The price of a bicycle will depend on many different factors and can range from a few hundred to several thousand euros for each category of bicycle. A more expensive bike will definitely be lighter, roll easier, have a wider gear range - all of which will increase your riding fun and, very likely, your time on the bike!